In recent years, the needs for hybrid electric vehicles, electric vehicles, and others have been increased. Accordingly, motors have been studied to be used for the driving power of vehicles. Such motors to be mounted in the vehicles are demanded for high power and downsizing. Particularly, hybrid electric vehicles are strictly demanded for size reduction in view of the placement of a motor in an engine room. Therefore, various studies have been made to achieve downsizing and high power of motors.
For instance, Patent Literature 1 listed below discloses a stator including a plurality of unit coils each of which is formed of a rectangular conductor wire (a flat conductor wire) wound in plural turns. The unit coils are mounted in slots of the stator core and connected in respective phases to constitute the distributed winding type multi-phase coil. Each unit coil includes a straight (or linear) portion to be inserted in a slot of the stator core and coil end portions to be placed on end faces of the stator core. On each coil end portion, each unit coil is formed with a crank-shaped portion including no twisting. Each unit coil is mounted in the stator core in a concentrically wound form by striding over slots for different phases.
As disclosed in Patent Literature 1, the pattern of the multi-phase coil of the stator includes a concentrated winding type and a distributed winding type. The concentrated winding type is achieved by winding a coil (a wire) in concentrating manner on each teeth portion of the stator core. The distributed winding type is achieved by winding a plurality of unit coils each striding over some slots of the stator core so that the unit coils of the different phase or the same phase overlap one on another on each coil end. The stator including the concentrated winding type multi-phase coil could reduce the size of the coil ends. This configuration is effective in downsizing and improvement in efficiency of a motor. The stator core including the distributed winding type multi-phase coil could make a rotating magnetic field inside the stator approximate to a sine wave. This realizes power and lower noise than the concentrated winding type. Both types adopt the flat conductor wire as a coil wire to enhance a coil space factor of the slot, thereby achieving high power of the motor.
On the other hand, Patent Literature 2 listed below discloses a stator constituted of a multi-phase coil wound on a stator core in a single-phase concentrically winding manner. The multi-phase coil includes a first U-phase coil, a second U-phase coil, a first V-phase coil, a second V-phase coil, a first W-phase coil, and a second W-phase coil, which are unit coils respectively. The first U-phase coil is made by winding a first wire coil, a second wire coil, and a third wire coil in a single-phase concentrically winding manner. A winding end portion of the first wire coil is connected with a winding start portion of the second wire coil, a winding end portion of the second wire coil is connected with a winding start portion of a third wire coil. That is, the first U-phase coil consists of the concentrically wound wire coils arranged in three layers to form a single unit coil. A winding start portion of the first wire coil and a winding end portion of the third wire coil are used as a pair of connection end portions to be connected respectively to a second U-phase coil. The second U-phase coil, the first V-phase coil, the second V-phase coil, the first W-phase coil, and the second W-phase coil are configured in the same manner as above.